Enhancing the functional value of watermelon through study of bioactive compounds and grafting potential in Armenia

Background: Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a nutritionally valuable fruit, rich in bioactive compounds such as lycopene, β-carotene, phenolic compounds, flavonoids, citrulline, cucurbitacin, vitamins (B, A, C), and essential minerals. These components contribute to numerous health benefits, including antibacterial, anti-atherosclerotic, cardiovascular protective, antioxidant, and anti-inflammatory effects. This makes watermelon increasingly significant both nutritionally and economically. In Armenia, watermelon is a highly demanded crop; however, its cultivation in the Armavir Marz is frequently challenged by biotic and abiotic stresses, resulting in wilting and yield reduction. Grafting technology offers an effective and environmentally friendly solution to enhance yield, improve fruit quality, and increase resistance to various stresses. Objective: This study aimed to evaluate the impact of grafting on watermelon yield, disease resistance, and the content of key bioactive compounds, with the goal of enhancing its functional value. Methods: Seven watermelon F1 hybrids (ES75077, ES75095, ES75111, ES75126, ES75127, ES75169, ES75171) were used as scions and grafted onto the bottle gourd (Lagenaria siceraria) rootstock ES101 from the Ergon Seed Company using the tongue approach. Throughout the growing season, phenological observations and yield component assessments were conducted. The content of ascorbic acid (AA), total phenolic content (TPC), lycopene, and sugars was determined spectrophotometrically. The presence of Fusarium oxysporum was detected using real-time quantitative Polymerase Chain Reaction (qPCR) to quantify infection rates and assess the resistance of grafted combinations. All experimental data were statistically analyzed using ANOVA. Results: Grafting significantly increased the productivity of all watermelon varieties, up to 2.1 times compared to non-grafted plants. The most notable increases were observed in variants ES75127 (2.1-fold) and ES75171 (1.9-fold). This enhanced yield is primarily attributed to an increase in average fruit weight (ranging from 8 kg to 14 kg) and a higher number of fruits per plant, likely due to the rootstock's robust system enhancing water and nutrient uptake. Furthermore, grafting substantially improved the fruits’ nutritional quality. Lycopene content in grafted plants increased by 1.1 to 2.3 mg/100 g fresh weight compared to non-grafted counterparts, with variants ES75127 and ES75111 demonstrating particularly high levels of lycopene, ascorbic acid, and total phenolic content. Phytosanitary assessments confirmed that grafted plants exhibited significantly lower infection rates of Fusarium oxysporum, thereby enhancing resistance and mitigating disease impact, especially in lines ES75127 and ES75111. Novelty: This is the first study to introduce watermelon grafting in Armenia, offering a sustainable and eco-friendly approach to combat soil-borne diseases and improve yields. Grafted plants not only display enhanced vegetative vigor but also show elevated levels of bioactive compounds, thereby improving both functional food potential and agricultural performance. Conclusion: Grafting is an effective strategy for enhancing both the productivity and nutritional profile of watermelon, especially regarding bioactive compounds associated with health benefits. Our comparative analysis identified the grafted variant ES75127 as the most productive, excelling in lycopene, ascorbic acid, total phenolics, and sugar content, while also exhibiting strong resistance to Fusarium oxysporum. Keywords: watermelon, lycopene, ascorbic acid, total phenols, Fusarium resistance, productivity